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Atmospheric chemistry of VOCs and NOx

Aerosols are of central importance for atmospheric chemistry and physics, the biosphere, climate, and public health. The airborne solid and liquid particles in the nanometer to micrometer size range influence the energy balance of the Earth, the hydrological cycle, atmospheric circulation, and the abundance of greenhouse and reactive trace gases. Moreover, they play important roles in the reproduction of biological organisms and can cause or enhance diseases. The primary parameters that determine the environmental and health effects of aerosol particles are their concentration, size, structure, and chemical composition. These parameters, however, are spatially and temporally highly variable. The quantification and identification of biological particles and carbonaceous components of fine particulate matter in the air (organic compounds and black or elemental carbon, respectively) represent demanding analytical challenges. This Review outlines the current state of knowledge, major open questions, and research perspectives on the properties and interactions of atmospheric aerosols and their effects on climate and human health.

Atmospheric aerosols: composition, transformation, climate and health effects.

[1] A global set of present plate boundaries on the Earth is presented in digital form. Most come from sources in the literature. A few boundaries are newly interpreted from topography, volcanism, and/or seismicity, taking into account relative plate velocities from magnetic anomalies, moment tensor solutions, and/or geodesy. In addition to the 14 large plates whose motion was described by the NUVEL-1A poles (Africa, Antarctica, Arabia, Australia, Caribbean, Cocos, Eurasia, India, Juan de Fuca, Nazca, North America, Pacific, Philippine Sea, South America), model PB2002 includes 38 small plates (Okhotsk, Amur, Yangtze, Okinawa, Sunda, Burma, Molucca Sea, Banda Sea, Timor, Birds Head, Maoke, Caroline, Mariana, North Bismarck, Manus, South Bismarck, Solomon Sea, Woodlark, New Hebrides, Conway Reef, Balmoral Reef, Futuna, Niuafo'ou, Tonga, Kermadec, Rivera, Galapagos, Easter, Juan Fernandez, Panama, North Andes, Altiplano, Shetland, Scotia, Sandwich, Aegean Sea, Anatolia, Somalia), for a total of 52 plates. No attempt is made to divide the Alps-Persia-Tibet mountain belt, the Philippine Islands, the Peruvian Andes, the Sierras Pampeanas, or the California-Nevada zone of dextral transtension into plates; instead, they are designated as “orogens” in which this plate model is not expected to be accurate. The cumulative-number/area distribution for this model follows a power law for plates with areas between 0.002 and 1 steradian. Departure from this scaling at the small-plate end suggests that future work is very likely to define more very small plates within the orogens. The model is presented in four digital files: a set of plate boundary segments; a set of plate outlines; a set of outlines of the orogens; and a table of characteristics of each digitization step along plate boundaries, including estimated relative velocity vector and classification into one of 7 types (continental convergence zone, continental transform fault, continental rift, oceanic spreading ridge, oceanic transform fault, oceanic convergent boundary, subduction zone). Total length, mean velocity, and total rate of area production/destruction are computed for each class; the global rate of area production and destruction is 0.108 m2/s, which is higher than in previous models because of the incorporation of back-arc spreading.

An updated digital model of plate boundaries

SCIAMACHY (Scanning Imaging Absorption Spectrometer for Atmospheric Chartography) is a spectrometer designed to measure sunlight transmitted, reflected, and scattered by the earth’s atmosphere or surface in the ultraviolet, visible, and near-infrared wavelength region (240–2380 nm) at moderate spectral resolution (0.2–1.5 nm, λ/Δλ ≈ 1000–10 000). SCIAMACHY will measure the earthshine radiance in limb and nadir viewing geometries and solar or lunar light transmitted through the atmosphere observed in occultation. The extraterrestrial solar irradiance and lunar radiance will be determined from observations of the sun and the moon above the atmosphere. The absorption, reflection, and scattering behavior of the atmosphere and the earth’s surface is determined from comparison of earthshine radiance and solar irradiance. Inversion of the ratio of earthshine radiance and solar irradiance yields information about the amounts and distribution of important atmospheric constituents and the spectral reflecta...

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SCIAMACHY: Mission Objectives and Measurement Modes

A model for the photochemistry of the global troposphere constrained by observed concentrations of H2O, O3, CO, CH4, NO, NO2, and HNO3 is presented. Data for NO and NO2 are insufficient to define the global distribution of these gases but are nonetheless useful in limiting several of the more uncertain parameters of the model. Concentrations of OH, HO2, H2O2, NO, NO2, NO3, N2O5, HNO2, HO2NO2, CH3O2, CH3OOH, CH2O, and CH3CCl3 are calculated as functions of altitude, latitude, and season. Results imply that the source for nitrogen oxides in the remote troposphere is geographically dispersed and surprisingly small, less than 107 tons N yr−1. Global sources for CO and CH4 are 1.5 × 109 tons C yr−1 and 4.5 × 108 tons C yr−1, respectively. Carbon monoxide is derived from combustion of fossil fuel (15%) and oxidation of atmospheric CH4 (25%), with the balance from burning of vegetation and oxidation of biospheric hydrocarbons. Production of CO in the northern hemisphere exceeds that in the southern hemisphere by about a factor of 2. Industrial and agricultural activities provide approximately half the global source of CO. Oxidation of CO and CH4 provides sources of tropospheric O3 similar in magnitude to loss by in situ photochemistry. Observations of CH3CCl3 could offer an important check of the tropospheric model and results shown here suggest that computed concentrations of OH should be reliable within a factor of 2. A more definitive test requires better definition of release rates for CH3CCl3 and improved measurements for its distribution in the atmosphere.

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Tropospheric chemistry: A global perspective

The Global Ozone Monitoring Experiment (GOME) is a new instrument aboard the European Space Agency’s (ESA) Second European Remote Sensing Satellite (ERS-2), which was launched in April 1995. The main scientific objective of the GOME mission is to determine the global distribution of ozone and several other trace gases, which play an important role in the ozone chemistry of the earth’s stratosphere and troposphere. GOME measures the sunlight scattered from the earth’s atmosphere and/or reflected by the surface in nadir viewing mode in the spectral region 240–790 nm at a moderate spectral resolution of between 0.2 and 0.4 nm. Using the maximum 960-km across-track swath width, the spatial resolution of a GOME ground pixel is 40 × 320 km2 for the majority of the orbit and global coverage is achieved in three days after 43 orbits. Operational data products of GOME as generated by DLR-DFD, the German Data Processing and Archiving Facility (D-PAF) for GOME, comprise absolute radiometrically calibrated e...

/pdf/the-global-ozone-monitoring-experiment-gome-mission-concept-4qlt0gaapi.pdf

The Global Ozone Monitoring Experiment (GOME): Mission Concept and First Scientific Results

The nitrate radical: Physics, chemistry, and the atmosphere

Formaldehyde mixing ratios are reported for rural areas around Julich and for maritime air at the north coast of Germany. The measurements were made using a ground-based UV-optical absorption technique which allowed the simultaneous determination of CH2O, NO2, and O3 with detection limits of 0.1, 0.1, and 1 ppb, respectively. In Julich, which may be regarded as typical for central European background atmosphere, mixing ratios varied from 0.1 to 6.5 ppb from May through October 1978. In maritime air under conditions when photochemical equilibrium was expected, formaldehyde concentrations of 0.2 ppb were observed, which can be accounted for by photochemical oxidation of methane alone. However, the high concentrations of formaldehyde found at Julich indicate other sources of formaldehyde.

Simultaneous measurement of atmospheric CH2O, O3, and NO2 by differential optical absorption

HNO2 was investigated by long path optical absorption at three sites in Western Europe. It vas definitely identified and measured in moderately polluted air at Julich. Mixing ratios as high as 0.8 ppb were observed before sunrise. After sunrise the HNO2 is photolyzed and considerable amounts of OH are produced. The formation of HNO2 is unclear and possible reactions are discussed.

Detection of nitrous acid in the atmosphere by differential optical absorption

The nitrate radical, NO3, has been identified and measured for the first time in the polluted troposphere using long path (970 and 750 m) differential optical absorption spectroscopy at two sites in the Los Angeles basin. NO3 concentrations of up to 355 ppt were measured using the strong NO3 absorption bands at 623 and 662 nm. During pollution episodes from September 11 to September 19, 1979 concentrations increased sharply after sunset and peaked about one hour later at ∼ 20:00 (PDT). In many other cases peak concentrations were much lower and sometimes below the detection limit of several ppt. Possible sinks for the NO3 radical under polluted conditions are considered, including reaction with NO, reaction with organic species, and the hydrolysis of N2O5 for which a new upper limit rate constant is derived.

Dieter Perner

Papers

The Global Ozone Monitoring Experiment (GOME): Mission Concept and First Scientific Results

The nitrate radical: Physics, chemistry, and the atmosphere

Simultaneous measurement of atmospheric CH2O, O3, and NO2 by differential optical absorption

Detection of nitrous acid in the atmosphere by differential optical absorption

Detection of NO3 in the polluted troposphere by differential optical absorption